1. Field of the Invention
The present invention relates to an image projecting apparatus and an image projecting method.
2. Description of the Related Art
As a result of the growth of electronic information media, there are increasing occasions where an image projecting apparatus (also referred to as “a projector”) is utilized. A typical projector comprises an illumination optical system including a light source, and a light modulating device, such as a liquid crystal light valve, that modulates a flux of light emitted by the illumination optical system in accordance with image information that is entered externally. It also comprises a projection optical system, such as a projection lens, for projecting the flux of light modulated by the light modulating device on a screen as an enlarged image. Among others, a liquid crystal projector that employs an LCD device as a light modulating device is well-known. The liquid crystal projector, by which the screen size is readily adjustable and which has excellent color reproducibility, is widely used for conference room presentation purposes, for example.
The liquid crystal projector employs the LCD device as an image generator to generate an image which is projected by the projection optical system on a screen with magnification. The LCD device can be categorized as a scattering type, such as the polymer dispersed liquid crystal (PDLC) mode, or a polarizing type, such as the twisted nematic (TN) mode, based on its liquid crystal mode. It can also be classified as a transmission type or a reflection type, based on whether it transmits or reflects the illuminating light. The liquid crystal projector can be a single-plate type or a three-plate type, for example, depending on the number of liquid crystal panels used. In the case of a transmission-type liquid crystal projector, of which the outline of an optical arrangement and structure is shown in FIG. 1, a light source 1 emits a flux of light that is incident on a liquid crystal light modulator 3, which generates an image by determining whether the light flux should be transmitted on a pixel unit region basis. The thus generated image is then focused by a projection lens 4 onto a screen. The liquid crystal light modulator 3 is fed with an image signal 14 representing image information on a pixel unit basis. Lately, a digital micromirror array device (DMD) has also been developed as a light modulating device, other than the LCD device.
As the aforementioned type of projector becomes more and more widespread, the demand to simplify and reduce the size of the projector is rapidly increasing. In order to address such demand, one important issue is how to reduce the size or weight of the projection lens forming the projection optical system. The size or weight of the projection lens can be effectively reduced by reducing the number of individual lenses of which the projection lens is composed. However, reducing the number of the individual lenses generally results in a decrease in resolution, or degradation in imaging properties in terms of, e.g., distortion, chromatic aberration of magnification, and aberration.
With regard to the problem of aberration associated with the projection lens, a method to reduce such aberration in an image projected on the screen has been proposed. In this method, various aberrations that could develop due to the projection lens are estimated in the design stage, and the shape or structure of the light modulating device is adjusted to compensate in advance for the aberrations expected to be produced by the projection lens. For example, Japanese Patent No. 3264916 discloses a method whereby, in order to compensate for chromatic aberration, the size of the effective area of the light modulating device for the production of an image is varied depending on the wavelength. Japanese Patent No. 3357026 discloses a light modulating device whose shape is distorted or curved in a manner corresponding to the distortion or curvature caused by the projection lens.
As discussed above, various aberrations due to the projection lens can be reduced to some extent by appropriately designing the shape or structure of the light modulating device. However, such methods are still associated with the problem of how to prevent the decrease in resolution of the projection lens. When a projection lens is reduced in size or simplified, particularly for the purpose of reducing the size of the projector, its imaging performance tends to deteriorate at the peripheral portions of the image projected on a screen. With conventional methods, it has been difficult to compensate for such a decrease in imaging performance in such partial regions of the image.